The present invention generally relates to electrical wiring systems which are subject to fault conditions and, more particularly, to ground and line fault interrupters included in such electrical wiring systems to protect users from injury.
Electrical wiring systems are typically included in residential, commercial and industrial environments wherein electrical power is supplied to various components in the system. Generally, such electrical wiring systems include phase and neutral (or return) conductors, which when properly connected, supply electrical power to the system components.
Certain safety code requirements are in place for some electrical wiring systems wherein the safety codes require the installation of circuit protection devices that trip when certain electrical based faults occur. For example, in aviation electronics, it is desirable to have a circuit protection device in electrical wiring systems that are positioned near potential ignition sources, such as a fuel tank. One example of such a circuit protection device is a ground fault interrupter (GFI) that is responsive to the detection of ground faults.
Conventional ground fault interrupters typically use a sense transformer, such as a differential transformer, to sense a difference current in the phase and neutral conductors that pass through the transformer. The difference current is transferred to a secondary winding of the differential reference. Typically, the current at the secondary winding, known as the secondary current, is proportional to the difference current. Conventional GFI devices also include a ground/neutral transformer to detect ground faults.
Generally, when detecting ground faults from a difference current, a sense amplifier converts the secondary current to a voltage level. This voltage level is compared to two window detector reference voltages, and if one of the compared voltages exceeds a designed threshold or reference signal for a predetermined period of time, a trigger signal, representing a difference current ground fault, is generated. Generally, when detecting ground to neutral faults, the ground/neutral and sense transformers are coupled through external resistors and capacitors and a neutral wire ground loop, to form a positive feedback loop around the sense amplifier. The feedback loop causes the sense amplifier to oscillate at a frequency determined by the inductance of the secondary winding of the ground/neutral transformer and a capacitor. If the amplifier oscillates for predefined period of time, the trigger signal, representing a ground to neutral fault, is generated.
One problem in the art is that some electrical wiring systems have been designed without including a GFI device. Consequently, it would be highly desirable to retrofit such electrical wiring systems with circuitry to provide fault protection. Further, it would be desirable to retrofit such electrical wiring systems by minimally changing the existing electrical circuitry (i.e. no additional ground or neutral connections).
As can be seen, there is a need for a GFI adapter which can be implemented into existing electrical wiring systems.